Ok, finding this stupid error took me a whole day again!

apparently one has to create one world instance for each storage created. Now why is that not stated in the documentation? Who knows. Anyway, now using multiple redland models all over the place works! :)

Why did I not catch this before? Well, all tests worked. This only happened when, in nepomuk, I created a bunch of memory models.

No idea why there were never any problems with the unit tests.